The job of testing all types of weaponry on these Rolls Royce laden aircraft must have been phenominal, with retightening of bolts and ancillaries a frequent task!. If you bear in mind the air frames, especially the wing constructions where most of the ammo was stored, with the exception of the Mosquito, I am surprised you could here yourself talk!!
The Spitfire the "role model" leaped from 8 X .303 Brownings with 300 rounds a piece, to 2 X Hispano Cannons one in each wing. Down side was that when the cannon jammed which they often did in combat, the remaining cannon threw the aircraft well off course and off target. They then moved onto 2 x 0.5" Brownings to support this issue on the later Marks of the Spitfire/Hurricane, an unbelievable achievement in a short stressful five years of WW2 IMHO.